SparkFun RTK Express

The SparkFun RTK Express is an easy to use GNSS receiver for centimeter-level positioning. Perfect for surveying, logging, and all types of post processing, this preprogrammed device can also be used for autonomous driving, navigation, asset tracking and any other application where there is a clear view of the sky. The RTK Express can also be used as a base station. With the press of a button, two RTK Expresses can be used to create an RTK system capable of 14mm horizontal positional accuracy. The built-in Bluetooth® connection via an ESP32 WROOM enables the user to use the RTK Express with their choice of GIS application on a phone or tablet. The built in battery allows for over five hours of field use and is compatible with common USB battery banks.

We took all the lessons from the RTK Surveyor and built the RTK Express. The RTK Express is built upon the same ZED-F9P u-blox receiver as the original RTK Surveyor so you can expect the same incredible performance and rich feature set. The embedded display allows for immediate feedback of horizontal positional accuracy, satellites in view, logging status, survey-in status, battery level, Bluetooth® MAC, etc. The rocker switches found on the original have been replaced by keypad buttons. Sparkfun increased the battery to 1300mAh for a longer run time. The internal switches have been replaced by a digital Mux allowing for some really exciting applications including event triangulation. More ESD protection was added to protect the RF path, and Sparkfun even threw in an accelerometer for digital leveling in the field.

This device can be used in four modes:

• GNSS Positioning (~30cm accuracy)
• GNSS Positioning with RTK (1.4cm accuracy)
• GNSS Base Station
• GNSS Base Station NTRIP Server

In Position mode the device receives L1/L2 signals from a user-provided antenna and the high-grade GNSS receiver provides lat/long and altitude with accuracies around 300mm.

In Positioning with RTK mode the device receives L1/L2 signals from the antenna and correction data from a base station. The correction data can be obtained from a cellular link to online correction sources or over a radio link to a second RTK Surveyor/Express setup as a base station.

In Base Station mode the device is mounted to a temporary position (like a tripod) and begins transmitting correction data over a radio or Internet connection. A base is often used in conjunction with a second unit set to 'Positioning with RTK' to obtain the 14mm relative accuracy. The RTK Surveyor and RTK Express are interchangeable as a Base Station; an RTK Surveyor can be a base for an RTK Express and vice versa.

In Base Station NTRIP Server mode the device is mounted to a semi or permanently fixed position (like a roof) and connects over WiFi to transmit the correction data to a NTRIP caster so that any rover can access the correction data over a cellular or Internet connection. This type of base is a very easy way to set up a very precise absolute correction source.

Two cables are provided with the RTK Express allowing a user to plug in our easy to use Serial Telemetry Radios or their own radio link. If a local correction source is within 10km, a user can also use their phone to provide correction data over the Bluetooth® link (no external radio needed!).

We are undergoing FCC/CE EMI and safety testing for the RTK Express. Once complete the RTK Express will become a mainstream SparkFun product. For now, this is fully capable, fully programmed, but consider it a device in development.

Changes: This version (which replaces SPX-18019) uses a reinforced edge mount SMA connector for better resiliency when a fixed 'stub' antenna is used.

Note: The SparkFun RTK Express is just the enclosed device and does NOT include an antenna, serial telemetry radio, or associated mounting pieces. These items will need to be purchased separately from the Hookup Accessories below.

Get Started With the SparkFun RTK Express Guide

Experimental Product: SparkX products are rapidly produced to bring you the most cutting edge technology as it becomes available. These products are tested but come with no guarantees. Live technical support is not available for SparkX products. Head on over to our forum for support or to ask a question.

GNSS Receiver: ZED-F9P

• Concurrent reception of GPS, GLONASS, Galileo and BeiDou
• Receives both L1C/A and L2C bands
• Current: 68mA - 130mA (varies with constellations and tracking state)
• Time to First Fix: 25s (cold), 2s (hot)
• Max Navigation Rate:
  • PVT (basic location over UBX binary protocol) - 25Hz
  • RTK - 20Hz
  • Raw - 25Hz
• Horizontal Position Accuracy:
  • 2.5m without RTK
  • 0.010m with RTK
• Max Altitude: 50km (31 miles)
• Max Velocity: 500m/s (1118mph)

Bluetooth® Transceiver: ESP32 WROOM

• Xtensa® dual-core 32-bit LX6 microprocessor
• Up to 240MHz clock frequency
• 4MB of flash storage
• 520kB internal SRAM
• Integrated 802.11 BGN WiFi transceiver
• Integrated dual-mode Bluetooth® (classic and BLE)
• Hardware accelerated encryption (AES, SHA2, ECC, RSA-4096)
• 2.5 µA deep sleep current

Overall Device

• Internal Battery: LiPo 1300mAh with 500mA charging
• Radio Port: 3.3V TTL Serial (57600bps RTCM TX/RX)
• Data Port: 3.3V TTL Serial (115200bps NMEA)
• Embedded OLED Display for available satellites, data logging, and more.
• Push button controls
• Weight: 162g (entire device including battery)
• Dimensions: 132mm x 101mm x 32mm (5.2in x 3.9in x 1.2in)
• 1x Qwiic Connector

• Schematic
• Hookup Guide
• Firmware Repo
• Hardware Repo
• Certified OSHW: US002050